Image sensing scheme capable of saving more power as well as avoiding image lost and also simplifying complex image recursive calculation

ABSTRACT

A method of an image sensor circuit includes: providing an event camera comprising at least one pixel unit; using the event camera to sense at least one current pixel value of the at least one pixel unit to detect whether at least one pixel value changes; when the at least one pixel value changes, using the event camera to trigger the digital processing circuit when the digital processing circuit is in a power saving mode and transmit information of the at least one pixel value to the digital processing circuit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 17/376,127, filed on Jul. 14, 2021, which is a continuation-in-partof U.S. application Ser. No. 17/151,625, filed on Jan. 18, 2021, whichis a continuation application of U.S. application Ser. No. 16/833,677,filed on Mar. 30, 2020, which is a continuation application of U.S.application Ser. No. 16/018,025, filed on Jun. 25, 2018, which is acontinuation-in-part of U.S. application Ser. No. 15/854,697, filed onDec. 26, 2017. The contents of these applications are incorporatedherein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to an image monitoring scheme, and moreparticularly to an image sensor circuit, an image sensor apparatus, andcorresponding methods.

2. Description of the Prior Art

Please refer to FIG. 1 . FIG. 1 is a monitoring system 50 in prior art.The monitoring system 50 includes a passive detector 52 and an imagedetection device 54 electrically connected to an external host 56. Thepassive detector 52 can transmit a triggering signal to the externalhost 56 while detecting temperature variation, the external host 56wakes up by the triggering signal and then actuates the image detectiondevice 54, and the image detection device 54 executes an exposureadjustment while being actuated and starts to capture a monitoring imageor to record monitoring video. Thus, even though the passive detector 52detects the temperature variation, the image detection device 54captures the monitoring image at a later time in relation to atransmission period of the triggering signal, wakeup periods of theexternal host 56 and the image detection device 54, and an exposureadjustment period of the image detection device 54, so that themonitoring system 50 cannot record the monitoring video right after thepassive detector 52 detects an unusual state.

SUMMARY OF THE INVENTION

Therefore one of the objectives of the invention is to provide an imagesensor circuit, an image sensor apparatus, and corresponding methods, tosolve the problems.

According to embodiments of the invention, an image sensor circuit isdisclosed. The image sensor circuit is to be externally coupled to adigital processing circuit that is arranged for performing a motiondetection. The image sensor circuit comprises an event camera whichcomprises at least one pixel unit. The event camera is arranged forsensing at least one current pixel value of the at least one pixel unitto detect whether at least one pixel value changes. When the at leastone pixel value changes, the event camera triggers the digitalprocessing circuit when the digital processing circuit is in a powersaving mode and transmits information of the at least one pixel value tothe digital processing circuit.

According to the embodiments, an image sensor apparatus is disclosed.The apparatus comprises the above-mentioned image sensor circuit and thedigital processing circuit. The digital processing circuit uses theinformation of the at least one pixel value and a last data frame storedin the digital processing circuit to generate a current data frame.

According to the embodiments, a method of an image sensor circuit to beexternally coupled to a digital processing circuit that is arranged forperforming a motion detection is disclosed. The method comprises:providing an event camera comprising at least one pixel unit; using theevent camera to sense at least one current pixel value of the at leastone pixel unit to detect whether at least one pixel value changes; whenthe at least one pixel value changes, using the event camera to triggerthe digital processing circuit when the digital processing circuit is ina power saving mode and to transmit information of the at least onepixel value to the digital processing circuit.

According to the embodiments, a method of an image sensor apparatus isdisclosed. The method comprises: providing a digital processing circuitexternally coupled to the image sensor circuit to perform a motiondetection; and using the information of the at least one pixel value ofclaim 1 and a last data frame stored in the digital processing circuitto generate a current data frame.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a monitoring system 50 in prior art.

FIG. 2 is a block diagram of a motion detection device according to anembodiment of the present invention.

FIG. 3 is a flow chart of a motion detection method applied to themotion detection device according to the embodiment of the presentinvention.

FIG. 4 is a flow chart of a motion detection method applied to themotion detection device according to the embodiment of the presentinvention.

FIG. 5 is a waveform diagram of a frame rate executed by an imagecapturing unit according to the embodiment of the present invention.

FIG. 6 is a functional block diagram of a smart motion detection deviceaccording to a first embodiment of the present invention.

FIG. 7 is a procedural diagram of the smart motion detection deviceaccording to the first embodiment of the present invention.

FIG. 8 is a functional diagram of the smart motion detection deviceaccording to a second embodiment of the present invention.

FIG. 9 is a procedural diagram of the smart motion detection deviceaccording to the second embodiment of the present invention.

FIG. 10 is a functional diagram of the smart motion detection deviceaccording to a third embodiment of the present invention.

FIG. 11 is a procedural diagram of the smart motion detection deviceaccording to the third embodiment of the present invention.

FIG. 12 is a flow chart of a determining method according to theembodiment of the present invention.

FIG. 13 is a block diagram of a monitoring system according to anembodiment of the invention.

FIG. 14 is a diagram showing three different operation scenarios of theportions/components of monitoring system in FIG. 13 .

FIG. 15 is a diagram showing two different operations for updating andgenerating data of a current frame for the digital processing circuit asshown in FIG. 13 .

FIG. 16 is a flowchart diagram of the operations of SMD that justentered the normal mode according to an embodiment of the invention.

DETAILED DESCRIPTION

Please refer to FIG. 2 . FIG. 2 is a block diagram of a motion detectiondevice 60 according to an embodiment of the present invention. Themotion detection device 60 can be matched with a passive detector 62 andan external host 64 to provide preferred smart motion detectingfunction. The motion detection device 60 is electrically connectedbetween the passive detector 62 and the external host 64. The passivedetector 62 is used to detect if a specific situation happened, such asa living thing passed by or a door opened, so as to trigger the motiondetection device 60 to analyze if a true event of the specific situationexisted, which means the living thing detected by the passive detector62 is identified as an expected object. When the true event isdetermined, the motion detection device 60 transmits related data forthe external host 64 to determine a security alarm.

In one embodiment, the passive detector 62 can be a temperaturedetector, such as an infrared detector, and the motion detection device60 can be selectively operated in a sleep mode or a wakeup mode. While amonitoring region is in an usual state, the passive detector 62 does notdetect temperature variation, the motion detection device 60 stays in asleep mode; while in an unusual state that the specific situationhappens (such like the living thing passed by), the passive detector 62detects the temperature variation and generates a triggering signal toswitch the motion detection device 60 from the sleep mode to a wakeupmode.

The motion detection device 60 can include an image capturing unit 66,an operating processor 68, a memory 70 and a lighting unit 72. Theoperating processor 68 can drive the image capturing unit 66 toalternatively switch between the sleep mode and the wakeup mode, andfurther can drive the image capturing unit 66 to optionally capturemonitoring images with low quality and high quality. In one embodiment,the lighting unit 72 can be actuated only while the image capturing unit66 captures image, so as to enhance the image capturing unit 66capturing images in a power efficiency manner.

The image capturing unit 66 may capture a background monitoring imagewith a low frame rate in the sleep mode, and capture a plurality ofmonitoring images with a high frame rate in the wakeup mode. Thebackground image could be captured in low quality, wherein thebackground image is used for auto-exposure control of the imagecapturing unit 66. The monitoring images could comprise a firstmonitoring image with the low quality and a second monitoring image withthe high quality, wherein the first monitoring image is used for theoperating processor 68 to identify if the true event is happened and thesecond monitoring image is used for the external host 64 to determinethe security alarm. The monitoring images captured by the imagecapturing unit 66 can be stored inside the memory 70, and further thehigh quality monitoring image can be transmitted to the external host64.

In this embodiment, the monitoring system utilizes the passive detector62 to detect the object passing through the monitoring region for astart, and then utilizes the motion detection device 60 to analyzewhether the passed object conforms to a predetermined condition (i.e.,true event). As a view range of the passive detector 62 has passerby andthe specific situation is identified, the motion detection device 60 isswitched to the wakeup mode by the passive detector 62 and determineswhether the passerby is the expected object (which means the human); ifso, the motion detection device 60 actuates the external host 64, andthe external host 64 identifies the object within the monitoring imagesto optionally drive the motion detection device 60 in a recording mode,to transmit monitoring video, to send out a warning, to shut down themotion detection device 60 and to awaken another motion detection device60′ electrically connected with the external host 64.

Please refer to FIG. 3 . FIG. 3 is a flow chart of a motion detectionmethod applied to the motion detection device 60 according to theembodiment of the present invention. First, step S200 and S202 areexecuted to startup the monitoring system, and the passive detector 62is utilized to detect the object within the view range. If the passivedetector 62 does not detect the temperature variation, step S204 isexecuted to keep the image capturing unit 66 in the sleep mode; if thepassive detector 62 detects the temperature variation, step S206 isexecuted that the passive detector 62 transmits the triggering signal toswitch the image capturing unit 66 from the sleep mode to the wakeupmode. Then, step S208 and step S210 are executed, the lighting unit 72can be actuated in accordance with surrounding illumination and theimage capturing unit 66 captures the first monitoring image (with thelow quality), the operating processor 68 simply analyzes the firstmonitoring image for determining whether to actuate the external host64.

In one embodiment, the image capturing unit 66 captures the low qualitymonitoring image by using partial pixels, such as to divide the pixelarray into a plurality of 2×2 pixel blocks and to use only one pixel ineach pixel block to capture the image. In another embodiment, the imagecapturing unit 66 captures image by all pixels and divides all pixels toseveral pixel block (such as 2×2 pixel block) so as to combine values inall pixels in each pixel block as a block value and generates the lowquality monitoring image by those block values.

In step S210, the operating processor 68 preferably analyzes a specificregion of interest (ROI) within the first monitoring image to determineactuation of the external host 64, dimensions of the specific region issmaller than the first monitoring image, so that the operating processor68 can rapidly acquire an image analysis result due to less datacalculation in ROI; the first monitoring image setting as a low qualitymonitoring image is helpful to speed up image analysis about thespecific region of interest. Position and dimensions of ROI arepreferably predefined by the user, for example, a door and a window aresituated in the first monitoring image, ROI can cover the pattern of thedoor to avoid the analysis result from being interfered by left shadowon the window, or ROI can cover edges of window for detecting a thiefclimbing into the window and also preventing the analysis result frombeing interfered by the left shadow; the position and dimensions of ROIfurther may be varied according to the analysis result. However, theoperating processor 68 may analyze an entire region within the firstmonitoring image to perform the step S210, which depends on designdemand. The said image analysis can be executed by identifying a patterncontour within the monitoring image, comparing feature point on themonitoring image, and analyzing intensity variation of the monitoringimage optionally.

As the object does not conform to the predetermined condition, suck likethe passerby within the monitoring image being the animal instead of thehuman, step S212 is executed to not actuate the external host 64, andthe image capturing unit 66 may be passively or actively shut down toback the sleep mode. As the object conforms to the predeterminedcondition, which means the passerby within the monitoring image may bean unauthorized person, step S214 is executed to actuate the externalhost 64 and the image capturing unit 66 starts to capture the secondmonitoring image with the high quality, and the second monitoring imagecan be captured as static images format or a continuing video format andcan be stored inside the memory 70. Next, step S216 is executed that theexternal host 64 receives the second monitoring image and utilizes imagerecognition algorithm to precisely analyze the object within the secondmonitoring image.

The second monitoring image does not conform to a predeterminedthreshold, which means the object is not the unauthorized person, stepS218 is executed to shut down the motion detection device 60 passivelyor actively for energy economy; the second monitoring image conforms tothe predetermined threshold, hence the object is defined as theunauthorized person, step S220 is executed that the external host 64 canswitch the motion detection device 60 into the recording mode, themotion detection device 60 transmits the monitoring video outwardly forbackup, and the other motion detection devices 60′ can be simultaneouslyawaken for overall monitoring. Therefore, the passive detector 62 cannotdirectly actuate the external host 64 while detecting the object, themotion detection device 60 wakes up by trigger of the passive detector62 to capture the first monitoring image, and the external host 64 isactuated in accordance with the low quality image analysis of the firstmonitoring image through the motion detection device 60.

The motion detection device 60 can begin to capture the secondmonitoring image while the external host 64 is actuated. The externalhost 64 has to spend a period of time on waking other motion detectiondevices, the second monitoring image can record any doubtful eventinside the monitoring region before the other motion detection devicesare awaken, which means the monitoring system does not miss the doubtfulevent in a term between a detection timing of the passive detector 62and a wakeup timing of the other motion detection devices. The firstmonitoring image with the low quality is used by the motion detectiondevice 60 to determine existence of the object, the existencedetermination is rough computation and may be affected by noise, and thesecond monitoring image with the high quality is used by the externalhost 64 to analyze the accurate motion detection of the object, such asface recognition.

The present invention further provides an exposure adjustment functionfor preferred operational efficiency of the motion detection device 60.Please refer to FIG. 4 and FIG. 5 . FIG. 4 is a flow chart of a motiondetection method applied to the motion detection device 60 according toanother embodiment of the present invention. FIG. 5 is a waveformdiagram of a frame rate executed by the image capturing unit 66according to the foresaid embodiment of the present invention. In theembodiment, steps having the same numeral as one of the above-mentionedembodiment have the same content, and a detailed description is omittedherein for simplicity. As the motion detection device 60 is not awakenby the passive detector 62, step S205 can be executed to periodicallyswitch the image capturing unit 66 to the wakeup mode in the low framerate, and the image capturing unit 66 in the wakeup mode can execute theexposure adjustment and capture a low quality background image. As themotion detection device 60 is awaken, step S207 is executed to transformthe image capturing unit 66 into the wakeup mode in the high frame rate,and later, the image capturing unit 66 still captures the monitoringimage with the low quality to compare with the background image fordetermining actuation of the external host 64.

For example, as shown in FIG. 5 , the image capturing unit 66 mayexecute the exposure adjustment and capture the background image oneframe per second (1 fps) while the motion detection device 60 is nottriggered by the passive detector 62, which means an exposure parameterof the image capturing unit 66 can be adjusted and the background imagecan be established at timing T1, T2, T3 and T4. While the passivedetector 62 triggers the motion detection device 60 into the wakeup modeat timing T5, the motion detection device 60 may capture the firstmonitoring images thirty frames per second (30 fps), the latestbackground image (captured at the timing T4) has the exposure parametersimilar to ones of the first monitoring image captured at the timing T5,so that the image capturing unit 66 in the wakeup mode is not in need ofthe exposure adjustment, and can immediately acquire the superiormonitoring image with suitable exposure parameters.

In conclusion, the motion detection device of the present invention iselectrically connected between the passive detector and the externalhost, and the motion detection device is utilized to actuate theexternal host while the passive detector triggers the motion detectiondevice switched from the sleep mode to the wakeup mode. As the motiondetection device is in the sleep mode, the motion detection device canbe awaken in the low frame rate or stay in the sleep mode to adjust theexposure parameter and to capture the background image; as the motiondetection device is switched to the wakeup mode, the motion detectiondevice is transformed into the high frame rate to capture the lowquality monitoring image. The motion detection device executes thesimple image analysis via ROI of the low quality monitoring image for astart for determining whether to actuate the external host; since themotion detection device actuates the external host, the motion detectiondevice captures and stores the high quality monitoring image, and thehigh quality monitoring image can be used by the external host for theaccurate image analysis and execution of related application programs.The motion detection device of the present invention can effectivelyeconomize start-up time of the monitoring system without waiting for awakeup period of the external host and an exposure adjustment period ofthe motion detection device.

Please refer to FIG. 6 and FIG. 7 . FIG. 6 is a functional block diagramof a smart motion detection device 80 according to a first embodiment ofthe present invention. FIG. 7 is a procedural diagram of the smartmotion detection device 80 according to the first embodiment of thepresent invention. The smart motion detection device 80 can include amemory 82, a processor 84 and a sensor array 86, which are threeseparate components or combined as one or two integrated components. Thesensor array 86 can be directly coupled to the memory 82 and furtherelectrically connected with the processor 84. The sensor array 86includes a plurality of light detecting pixels arranged in two-dimensionmanner to capture images. The processor 84 can be switched between asleep mode and a wakeup mode, and used to process an image captured bythe sensor array 86 to identify a particular event in the capturedimages, such as an unexpected object been captured in the capturedimages.

The image captured by the sensor array 86 may be pre-stored (i.e.,wrote) into the memory 82 or directly transmitted to the processor 84 inaccordance with modes of the processor 84 or an alarm signal resultedfrom motion detection. The memory 82 can have the image capacity ofpredefined quantity; when the memory 82 is full and a new image isprepared to pre-store, a former image can be removed for storing the newimage. The image processed by the processor 84 and the pre-stored imagein the memory 82 can be transmitted to an external storage module 88electrically connected with the smart motion detection device 80.

As the first embodiment shown in FIG. 7 , the processor 84 stays in thesleep mode when the smart motion detection device 80 is not activated.The sensor array 86 can include a comparator 90 adapted to generate thealarm signal when monitoring motion of an object. As the processor 84 isoperated in the sleep mode, the sensor array 86 continuously orintermittently captures a plurality of images (such as capture fiveimages in every 1 second), and the plurality of images are pre-storedinto the memory 82; in the meantime, the comparator 90 reads andcompares at least some of the pre-stored images I1 with a referenceimage. When intensity variation between one of the pre-stored images I1and the reference image is smaller than a predefined value, theprocessor 84 keeps in the sleep mode and the comparator 90 reads thenext pre-stored image I1 for a comparison with the reference image. Whenthe intensity variation is greater than the predefined value, thecomparator 90 can generate the alarm signal utilized to awake theprocessor 84 and further to pre-store the image captured by the sensorarray 86 into the memory 82. That is, the alarm signal is used to switchthe processor 84 from the sleep mode to the wakeup mode.

There has variety ways for the comparator 90 to compare the pre-storedimages I1 and the reference image, for example the comparator 90 couldcompare whole image range or only compare partial pixels for thepre-stored images I1 and the reference image. The comparator 90 couldcompare intensity summation of all pixels or partial pixels, in anotherway the comparator 90 could compare intensity of each pixel in wholeimage range or only partial pixels.

When the processor 84 is operated in the wakeup mode, a real-time imageI2 captured by the sensor array 86 is directly transmitted to theprocessor 84 for digital processing and may not be stored into thememory 82. The processor 84 in the wakeup mode may process the real-timeimage I2 and receive the pre-stored image I1 in the memory 82 by turns,or may receive the pre-stored image I1 after processing of the real-timeimage I2. A process of the real-time image I2 can precede that of thepre-stored image I1, so the smart motion detection device 80 is able tofocus on an instant situation within the monitoring area. The process ofthe pre-stored image I1 may be executed when the process of thereal-time image I2 is completed or paused. If an operating capability ofthe processor 84 is sufficient for mass data, the real-time image I2 andthe pre-stored image I1 can be processed alternately, hence the smartmotion detection device 80 can show detection results about the currentand previous period at the same time.

In some embodiments, the pre-stored images captured by the sensor array86 when the processor 84 is operated in the sleep mode can be pre-storedinto the memory 82, and the real-time images captured by the sensorarray 86 when the processor 84 is operated in the wakeup mode can betransmitted to the processor 84. In other embodiments, the processor 84and the sensor array 86 can be turned off under a non-working mode; whenthe smart motion detection device 80 receives a trigger signal, thesensor array 86 can capture and send the images to the memory 82directly, and then the processor 84 can send a request to the sensorarray 86 for receiving the captured images. The trigger signal may be analarm resulted from an external unit or a built-in unit of the smartmotion detection device 80.

In addition, at least one of an image quality and a frame rate of thesensor array 86 may be changed when the processor 84 is operated in thesleep mode or the wakeup mode. For example, as the processor 84 is inthe sleep mode, the sensor array 86 can capture the low-quality image orcapture the image in the low frame rate for comparing with the referenceimage. Transmission bandwidth and storage capability are economizedaccordingly. The alarm signal is generated because the intensityvariation between the low-quality image (or the image captured in thelow frame rate) and the reference image is greater than the predefinedvalue, so that the sensor array 86 starts to capture the high-qualityimage or capture the image in the high frame rate for pre-storing intothe memory 82, and simultaneously the processor 84 can be switched tothe wakeup mode. Then, the pre-stored high-quality image or thepre-stored image captured in the high frame rate in the memory 82 istransmitted to the processor 84 operated in the wakeup mode; thereforethe smart motion detection device 80 does not lose image informationbefore the processor 84 is in the wakeup mode.

Please refer to FIG. 8 to FIG. 11 . FIG. 8 is a functional diagram ofthe smart motion detection device 80′ according to a second embodimentof the present invention. FIG. 9 is a procedural diagram of the smartmotion detection device 80′ according to the second embodiment of thepresent invention. FIG. 10 is a functional diagram of the smart motiondetection device 80″ according to a third embodiment of the presentinvention. FIG. 11 is a procedural diagram of the smart motion detectiondevice 80″ according to the third embodiment of the present invention.In the embodiments, elements having the same numerals as ones of thefirst embodiment have the same functions, and a detailed description isomitted herein for simplicity.

In a possible embodiment, the smart motion detection device 80′ caninclude the memory 82, the processor 84, the sensor array 86′ and apassive sensor 92. The passive sensor 92 is electrically connected withthe processor 84 and the sensor array 86′. The processor 84 is kept inthe sleep mode and the sensor array 86′ is shut down when the passivesensor 92 does not detect any abnormal situation. As the passive sensor92 detects the motion of the object, the passive sensor 92 can generatethe alarm signal, and the alarm signal is used to drive the sensor array86′ and switch the processor 84 from the sleep mode to the wakeup mode.When the processor 84 is still in the sleep mode, the sensor array 86′can capture and transmit the pre-stored image I1 to the memory 82. Whenthe processor 84 is operated in the wakeup mode, the sensor array 86′can capture and transmit the real-time image I2 to the processor 84, andthe pre-stored image I1 in the memory 82 can be transmitted to theprocessor 84 accordingly.

The smart motion detection device 80 may have the non-working mode. Theprocessor 84 and the sensor array 86′ can be turned off under thenon-working mode. As the passive sensor 92 detects the motion of theobject and generates the alarm signal, the sensor array 86′ is triggeredby the alarm signal and starts to capture and send the pre-stored imageinto the memory 82. After that, the processor 84 can be switched to thewakeup mode and then sends the request to the sensor array 86′ forreceiving the pre-stored image.

In another possible embodiment, the smart motion detection device 80″can include the memory 82, the processor 84, the sensor array 86″ havingthe comparator 90, and the passive sensor 92. The passive sensor 92 canactivate the sensor array 86″ when detecting the abnormal situation. Theactivated sensor array 86″ can capture and transmit the pre-stored imageI1 to the memory 82, and the comparator 90 can compare the pre-storedimage I1 with the reference image for determining whether to switch onthe processor 84. The comparator 90 is utilized to identify the abnormalsituation. If the intensity variation between the pre-stored image I1and the reference image is smaller than the predefined value, theabnormal situation may be resulted from noise and the processor 84 isnot switched on. If the intensity variation is greater than thepredefined value, the abnormal situation can be defined as someone orsomething intruding into the monitoring area of the smart motiondetection device, so that the processor 84 is switched to the wakeupmode for recording. As the processor 84 is operated in the wakeup mode,the real-time image I2 captured by the sensor array 86″ and thepre-stored image I1 in the memory 82 can be transmitted to the processor84 and then to the external storage module 88 for the digitalprocessing.

Please refer to FIG. 12 . FIG. 12 is a flow char of a determining methodaccording to the embodiment of the present invention. The determiningmethod illustrated in FIG. 12 can be suitable for the smart motiondetection devices shown in FIG. 6 to FIG. 11 . First, steps S800 andS802 are executed to start the determining method and to monitor themotion of the object. The said monitoring function can be applied by thesensor array 86, 86′ and 86″ or the passive sensor 92. As there is notabnormal situation, step S804 is executed to keep the processor 84 inthe sleep mode; as the motion of the object is detected, steps S806 andS808 are executed to generate the alarm signal for enabling theprocessor 84 and capturing the image via the sensor array 86, 86′ and86″. When the processor 84 is not operated in the wakeup mode, step S810is executed that the sensor array 86, 86′ or 86″ can produce thepre-stored image I1 in the memory 82. When the processor 84 is operatedin the wakeup mode, steps S812 and S814 are executed that the sensorarray 86, 86′ or 86″ can produce the real-time image I2, and both thepre-stored image I1 and the real-time image I2 can be transmitted to theprocessor 84.

After that, step S816 is executed that the processor 84 can analyze thereal-time image I2 captured by the sensor array 86, 86′ or 86″ whencapturing function of the sensor array 86, 86′ or 86″ is activated. Whenthe sensor array 86, 86′ or 86″ is not activated, probably owning to thedisappeared object or any other situations, step S818 is executed toanalyze the pre-stored image I1 inside the memory 82 by the processor84. It should be mentioned that the processor 84 not only can processthe real-time image I2 before the pre-stored image I1, but alsoalternately process the pre-stored image I1 and real-time image I2 inaccordance with the user's actual demand and the sufficient operatingcapability.

In conclusion, the alarm signal may be generated by the sensor array orthe passive sensor (which can be a thermal sensor, an accelerometer or agyro). The alarm signal is utilized to activate pre-storing operation ofthe sensor array and mode switching operation of the processor. When thealarm signal is received, the sensor array can be activated to capturethe pre-stored image at a first time and the pre-stored image istransmitted to the memory. For waiting a duration of the processorswitched from the sleep mode to the wakeup mode, the processor whichreceives the alarm signal can send a request to the sensor array for thereal-time image and the pre-stored image at a second time later than thefirst time, so that the pre-stored image from the memory are processedlater than the first time, and the real-time image is not stored intothe memory but directly transmitted to the processor for the digitalprocessing. Comparing to the prior art, the smart motion detectiondevice and the related determining method of the present invention caneffectively economize start-up time of the smart motion detection devicewithout waiting for a wakeup period of the processor.

Please refer to FIG. 13 in conjunction with FIG. 14 . FIG. 13 is a blockdiagram of a monitoring system 1300 according to an embodiment of theinvention. FIG. 14 is a diagram showing three different operationscenarios of the portions/components of monitoring system 1300 in FIG.13 . As shown in FIG. 13 , the monitoring system 1300 comprises threeportions, i.e. an analog integrated circuit (IC) portion/component, adigital IC portion/component, and a backend system device. In otherembodiments, the analog IC portion/component and digital ICportion/component may be integrated and implemented as an image sensorapparatus 1301, wherein the image sensor apparatus 1301 could be anintegrated circuit (IC). That is, such image sensor apparatus 1301 canbe divided into an analog portion (i.e. the analog IC portion/component)and a digital portion (i.e. the digital IC portion/component).

The analog IC portion/component is a collection of analogcircuits/components and for example is or comprises an image sensorcircuit such as an analog image sensor 1305 which comprises an eventcamera 1306 (or may be referred to as an event sensor) comprising atleast one pixel unit (i.e. one or more pixel units such as pixels orsub-pixels) such as active pixel unit(s). It should be noted that inpractice an event camera unit/circuit may comprise a pixel unit and beused to report changes in brightness as they occur and stay silentotherwise. That is, the event camera 1306 is used to detect whetherbrightness change(s) occur in one or more pixel units.

The digital IC portion/component is a collection of digitalcircuits/components and is or comprises a digital processing circuitcomprising a first image buffer 1311 and a motion detector such as asmart motion detector (SMD) 1312. When the event camera 1306 transmitsthe information of pixel image/value's change, the SMD 1312 can use suchpixel-level information to generate frame data, i.e. a frame-levelimage, and it can detect whether motion occurs. If it is determined thata motion occurs, then the SMD 1312 can generate an alert signal to thebackend system 1315. Instead, if no motions occur, the SMD 1312 does notgenerate the alert signal. SMD 1312 can accurately detect whether actualmotion occurs and filter out some undesired image fluctuations such asmotion images of shaking leaves or shaking grasses (not limited).

When receiving an alert signal sent from the digital processing circuit1310, the backend system 1315 is arranged to receive the image streams(i.e. frames) from the digital processing circuit 1310 and for exampleto start performing a video recording operation. The backend system 1315comprises a second image buffer 1316 and an external processor 1317 thatis externally coupled to the above-mentioned image sensor apparatus,i.e. the analog IC portion/component and digital IC portion/component.

The startup speed/time of the event camera 1306 (or the analog imagesensor circuit 1305) is much faster than that of the SMD 1312 (ordigital processing circuit 1310) and also much faster than that of theexternal processor 1317 (or the backend system device 1315). In oneembodiment, if no pixel values change, only the event camera 1306 (oronly the analog image sensor circuit 1305) is powered on and the othercircuits (i.e. the digital processing circuit 1310 and the backendsystem device 1315) are powered off or left in a power saving mode (suchas working under a low operating frequency), to save more power. Oncethe event camera 1306 (or the analog image sensor circuit 1305) detectsthat a pixel value changes, the SMD 1312 is awakened by a triggersignal, sent from the analog image sensor circuit 1305, to perform theabove-mentioned motion detection. Only when the motion detectionindicates that an actual motion occurs, the external processor 1317 inthe backend system device 1315 is awakened by a trigger signal, sentfrom the digital processing circuit 1310, to perform further imageprocessing and/or the video recording operation. If the event camera1306 includes a plurality of pixels, then the “no pixel values change”may refer to “the number of pixels that has pixel values change lessthan a first specific threshold,” and the “a pixel value changes” mayrefer to “a number of pixels that has a pixel value change exceed than asecond specific threshold”.

If the pixel value changes before the SMD 1312 is completely wakened,the pixel value(s) sensed by the image sensor circuit 1305 is/are storedinto the first image buffer 1311, and then will betransmitted/transferred to the SMD 1312 once the SMD 1312 is completelyawakened and able to receive the sensed pixel value(s). That is, whenthe event camera 1306 is going to send pixel value(s) to the digitalprocessing circuit 1310, the pixel value(s) will be stored into thefirst image buffer 1311 before the SMD 1312 is wakened and the firstimage buffer 1311 may store a plurality of pixel values from the eventcamera 1306 before the SMD 1312 is wakened. Then, similarly, when it isdetermined that the frame data formed by the sensed pixel value(s) isassociated with an actual motion event before the external processor1317 is completely wakened, the frame(s) or image stream(s) processed bythe digital processing circuit 1310 is/are stored into the second imagebuffer 1316, and then will be transmitted/transferred to the externalprocessor 1317 once the external processor 1317 is completely wakenedand able to receive the sensed frame(s) or image stream(s). Also, whenthe digital processing circuit 1310 is going to send frame(s) to thebackend system device 1315, the frame(s) will be stored into the secondimage buffer 1316 before the external processor 1317 is wakened and thesecond image buffer 1316 may store a plurality of frames from thedigital processing circuit 1310 before the external processor 1317 iswakened. By using the above-mentioned mechanisms and first/second imagebuffer(s), more power can be saved as well as image lost can be avoided.

As shown in FIG. 14 , for example, the analog image sensor circuit 1305is always awake (i.e. at an awake state or in a normal mode differentfrom a power saving mode) when it is supplied with power, tocontinuously or periodically detect whether the pixel value(s) of one ormore pixel units change. In a first operation scenario (but notlimited), if it is determined that no pixel values change, the analogimage sensor circuit 1305 does not send a trigger signal to wake up thedigital processing circuit 1310 and the backend system device 1315.Thus, the digital processing circuit 1310 and the backend system device1315 are kept asleep (i.e. at an asleep state or in the power savingmode). In this situation, the analog image sensor circuit 1305 does nottransmit pixel data to the digital processing circuit 1310 and backendsystem device 1315.

In a second operation scenario (but not limited), if it is determinedthat at least one pixel value changed, then the analog image sensorcircuit 1305 is arranged to send a trigger signal to wake up the digitalprocessing circuit 1310 and also send the sensed pixel data to thedigital processing circuit 1310. In the situation that the startupspeed/time of the first image buffer 1311 is much faster than that ofSMD 1312, the sensed pixel data can be temporarily stored in the firstimage buffer 1311 by using an image freeze operation before the SMD 1312is completely awakened. After the digital processing circuit 1310completely exits the power saving mode and enters the normal mode, thepixel data sensed by the analog image sensor circuit 1305 can bedirectly transmitted to the SMD 1312 without using the first imagebuffer 1311. In this situation, if it is determined that no actualmotions occur, then the digital processing circuit 1310 does not send analert signal to wake up the backend system device 1315 and also does nottransmit the generated frames or image streams to the backend systemdevice 1315.

It should be noted that the SMD 1312 can simultaneously receive andprocess both the stored pixel data of the first image buffer 1311 andthe incoming pixel data once the SMD 1312 completely enters the normalmode. For example (not limited), the SMD 1312 can employ a super highframe per second (HFPS) image processing frequency/rate to rapidlyprocess the accumulated pixel values stored in the first image buffer1311 and then synchronize the processed pixel values with the analogvalues of incoming pixel data. For instance, each time when the analogimage sensor circuit 1305 is called to sense pixel units, the SMD 1312is arranged to process the accumulated pixel values stored in the firstimage buffer 1311 and process the analog values of incoming pixel datain parallel until the first image buffer 1311 is empty.

In a third operation scenario (but not limited), the first image buffer1311 can be used to collect and store the pixel information (values ordifferences) of pixel units, which are transmitted from the analog imagesensor circuit 1305, to form and generate data of one or more completeframes. The SMD 1312 can determine whether an actual motion occurs basedon the generated frame data. If it is determined that an actual motionoccurs, the digital processing circuit 1310 is arranged to send an alertsignal to wake up the backend system device 1315 and also transmit thesensed frames or image streams to the backend system device 1315. Inthis situation, the sensed frames or image streams may be temporarilystored in the second image buffer 1316 by using the image freezeoperation before the backend system device 1315 is completely awakened.When the backend system device 1315 completely exits the power savingmode and enters the normal mode, sensed frames or image streams can bedirectly transmitted to the external processor 1317 without beingbuffered in the second image buffer 1316.

Refer back to FIG. 13 again. Specifically, to determine whether a pixelvalue (one or each pixel value) changes, the event camera 1306 isarranged for sensing/capturing the current pixel value of acorresponding pixel unit to detect whether the pixel value changes. Theevent camera 1306 for example senses or captures the current pixel valueof the pixel unit (as shown by S13051), and then it calculates a pixeldifference Diff between the sensed current pixel value and a referencepixel value of the pixel unit wherein the reference pixel value of suchpixel unit (as shown by S13052) can be a previous pixel value of thepixel unit sensed by the event camera at an earlier timing or an averageof a plurality of pixel values of the pixel unit sensed by the eventcamera at an earlier timing. Accordingly, for more or all pixel units,the event camera 1306 can capture a plurality of current pixel valuesand then calculate or generate a plurality of pixel differencesrespectively corresponding to a plurality of pixel units.

Then, the event camera 1306 determines whether the pixel value changedby comparing the pixel difference Diff with a pixel threshold TH (asshown by S13053). If the pixel difference Diff becomes higher than thepixel threshold TH, the event camera 1306 can determine that the pixelvalue changes. Instead, if the pixel difference Diff is not higher thanthe pixel threshold TH, the event camera 1306 determines that the pixelvalue does not change. It should be noted that in this embodiment thepixel value changing means that the pixel value varies significantlywhile the pixel value not changing means that the pixel value is notvaried or varies insignificantly.

When the pixel difference Diff becomes equal to or higher than the pixelthreshold TH, the event camera 1306 is arranged to generate and send atrigger signal to wake up the digital processing circuit 1310, send thecurrently counted value of a counter value N and the information/dataassociated with the currently captured pixel value to the digitalprocessing circuit 1310, update the reference pixel value by using thecurrently captured pixel value, and reset the counter value N as zero.The counter value N is configured as zero initially. If the SMD 1312 isnot in the normal mode, the currently counted value of the counter valueN and the information/data associated with the currently captured pixelvalue can be temporarily stored in the first image buffer 1311. Itshould be noted that the pixel difference Diff of the pixel unit iscalculated and updated each time after an exposure operation, performedupon the pixel unit, is finished to obtain its currently sensed pixelvalue. When the pixel difference Diff is not higher than the pixelthreshold TH, the event camera 1306 is arranged to increment oraccumulate the counter value N by one. In this situation, the eventcamera 1306 does not send the trigger signal, the currently countedvalue of the counter value N and, the information/data associated withthe currently captured pixel value.

The value of such counter value N is used to indicate the number oftimings of consecutive frames during which the pixel value of a pixelunit does not change. Equivalently, the counter value N, employed by theevent camera 1306, is arranged to determine a time interval between thepixel value of such pixel unit changing twice. It should be noted thatthe values of counter values N corresponding to different pixel unitsmay be identical, different, or may be partially different. In oneembodiment, a resultant counter value can be selected from the values ofcounter values N corresponding to different pixel units, and suchresultant counter value for example may be a smallest one in all thecounter values N corresponding to different pixel units. The selectedresultant counter value can be used to indicate a number of timings ofconsecutive frames during which the pixel values of all the pixel unitsdo not change.

Further, for example (but not limited), the frame rate may be equal to30 Hz, i.e. 30 frames in one second, and the counter value N may besequentially accumulated from zero to 30 during one second if it isdetermined that the pixel value of the pixel unit does not change duringsuch one second. In this situation, if it is then determined that thepixel value changes at a next frame timing, then the counter value Nwill not be counted to for example 31, and the event camera 1306 isarranged to generate a trigger signal to wake up the digital processingcircuit 1310 and to transmit the currently counted counter value (i.e.30) to the digital processing circuit 1310 before the counter value N isreset as zero. Also, at the same time, the event camera 1306 is arrangedto output information/data of the sensed/captured pixel value to thedigital processing circuit 1310.

The information/data of the sensed/captured pixel value which changesmay be transmitted from the analog image sensor circuit 1305 to thedigital processing circuit 1310 by using at least two different ways. Inone embodiment, the event camera 1306 may send an actual value of thecurrently captured pixel value to the digital processing circuit 1310,and the digital processing circuit 1310 can directly use the actualvalue to replace a corresponding value of a pixel unit in a previousframe to generate a current frame. Further, in other embodiments, theevent camera 1306 may send a difference value between the actual valueof the actually captured pixel value and the actual value of apreviously captured pixel value to the digital processing circuit 1310,and the digital processing circuit 1310 can add such difference valueinto a corresponding value of a pixel unit in a previous frame togenerate a current frame.

Refer to FIG. 15 . FIG. 15 is a diagram showing two different operationsfor updating and generating data of a current frame for the digitalprocessing circuit 1310 (or SMD 1312). For a pixel unit such as anactive pixel unit, data of a last previous frame can be stored in theSMD 1312 as a static frame FS even though some partial circuits withinSMD 1312 is powered off. Such static frame FS is generated by thedigital processing circuit 1310 at an earlier timing when the eventcamera 1306 detects the pixel value(s) change(s); that is, the staticframe FS is associated with the previous pixel value(s). As shown in afirst scenario of FIG. 15 , When it is determined that the pixel valueof the active pixel unit changes at a current frame timing, the eventcamera 1306 in the first scenario transmits the actual pixel value ofsuch active pixel unit to the image buffer 1311 of digital processingcircuit 1310 so that the image data associated with the change of pixelvalue can be stored in the image buffer 1311. Then, after SMD 1312completely enters the normal mode, the SMD 1312 can generate the currentframe FC based on the data of the static frame FS and the actual valueof the pixel value. In practice, the SMD 1312 is arranged to use theactual value to replace the previous value of such active pixel unit inthe static frame FS to generate the current frame FC.

Further, as shown in a second scenario of FIG. 15 , for the active pixelunit, when it is determined that the pixel value of the active pixelunit changes at the current frame timing, the event camera 1306 in thesecond scenario transmits the difference value of previously capturedand currently captured pixels corresponding to such active pixel unit tothe image buffer 1311 of digital processing circuit 1310. Then, afterSMD 1312 completely enters the normal mode, the SMD 1312 can generatethe current frame FC based on the data of the static frame FS and thedifference value. In practice, the SMD 1312 adds the difference valueinto the previous pixel value of the same active pixel unit in thestatic frame FS to generate the current frame FC.

In one embodiment, when the current frame FC is generated, the SMD 1312(or digital processing circuit 1310) is arranged to determine whether amotion occurs by generating one or more background frames based on thegenerated current frame FC and the counter value N and then comparingthe current frame FS with the background frames. In practice,information/data of a previous background frame can be stored in amemory circuit of the SMD 1312, and the information stored in the memorycircuit does not vanish even though the SMD 1312 is powered off. If theSMD 1312 has been kept in the normal mode, then the SMD 1312 may performa recursive moving average operation based on a previous backgroundframe and the current frame FC to generate a current background frame.For example (not limited), the current background frame can bedetermined by the following equation:

${FB}_{i} = \frac{{FB}_{i - 1} + {FC}}{2}$

wherein FB_(i) indicates data of the generated current background frameat a current frame timing i, FB_(i−1) indicates data of a previousbackground frame at a previous frame timing i−1 and FC indicates thecurrent frame (or called as a current data frame). Similarly, the nextbackground frame based on the recursive moving average operation can bedetermined by the following equation:

${FB}_{i + 1} = \frac{{FB}_{i} + {FC}^{\prime}}{2}$

wherein FC′ is a next data frame. Usually, in a monitoring system, thecurve corresponding to the background frames at the different frametimings will be convergenced into a stable background frame after aspecific training time period.

However, if the SMD 1312 just exited the power saving mode and no dataof the previous background frame FB_(i−1) can be used to generate thecurrent background frame FB_(i), then the SMD 1312 does not execute therecursive moving average operation. in this situation, the SMD 1312 isarranged to employ the counter value N to generate a weighting value andthen use the weighting value, current data frame FC, and a lastbackground frame FB_(i−N) stored in the memory circuit of SMD 1312 whenthe SMD 1312 becomes powered off. In this situation, the currentbackground frame FB_(i) can be determined by the following equation:

FB _(i) =∝×<FB _(i−N)+(1−∝)×FC

wherein ∝ is the weighting value generated based on the counter value N.in a simplified example (not limited), the weighting value ∝ may beequal to

$\frac{N - 1}{N}{or}{\frac{N}{N + 1}.}$

For instance, if the value N is equal to 30, then ∝ is equal to 29/30,and the current background frame FB_(i) can be determined by thefollowing equation:

${{FB}_{i} = {{\frac{29}{30} \times {FB}_{i - k}} + {\frac{1}{30} \times {FC}}}};$

and

alternatively, the current background frame FB_(i) may be determined bythe following equation:

${FB}_{i} = {{\frac{30}{31} \times {FB}_{i - k}} + {\frac{1}{31} \times {{FC}.}}}$

However, this is not meant to be a limitation of the invention. In otherwords, the weighting value ∝ can be dynamically determined based on thenumber of how many consecutive frames which a pixel unit's image/valuedoes not change. The calculation of using the counter value N todirectly generate the current background frame FB_(i) without executingthe recursive moving average operation becomes more simplified since inthis situation executing the recursive moving average operation needsrecursively calculating data of background frames FB_(i−1), . . . ,FB_(i−(N−1)).

To determine whether a motion occurs in the current frame FC, the SMD1312 is arranged to calculate a frame difference between the currentbackground frame FB_(i) and the current data frame FC, and then itcompares the frame difference with a motion threshold THM to determinewhether the motion occurs. When the frame difference becomes higher thanthe motion threshold THM, the SMD 1312 can determine that the motionoccurs and then generate an alarm signal to the backend system device1315.

The motion threshold THM for example may be a fixed threshold value orcan be dynamically adjusted. In one embodiment, the SMD 1312 can use acurve fitting operation to dynamically adjust the motion threshold THMaccording to a previous value of the motion threshold THM, the currentbackground frame FB_(i) the current data frame FC, and the counter valueN.

Then, for generating a next background frame FB_(i+1), the SMD 1312 forexample can execute the recursive moving average operation based on thegenerated current background frame FB_(i) and a next data frame FC′ whenthe next data frame FC′ is generated by using the information/data ofpixel value sent from the event camera 1306.

To make readers more clearly understand the operations mentioned above,FIG. 16 is provided. FIG. 16 is a flowchart diagram of the operations ofSMD 1312 that just entered the normal mode according to an embodiment ofthe invention. The steps are described in the following:

Step 1605: Start;

Step 1610: Generate current data frame FC according to the previousdata/static current FS and information/data of the pixel image/valuechanging (e.g. the actual pixel value or pixel difference value);

Step 1615: Generate a weighting value ∝ according to the counter value Nwhich is received from the event camera 1306 and buffered in the firstimage buffer 1311;

Step 1620: Generate a current background frame according to theweighting value ∝, the last background frame stored by the SMD 1312, andthe current data frame FC;

Step 1625: calculate a frame difference between the current data frameFC and the current background frame;

Step 1630: Dynamically update the motion threshold THM according to theprevious/original value of motion threshold THM, the last backgroundframe, and the current data frame FC;

Step 1635: Determine whether the frame difference is equal to or higherthan the motion threshold THM; if it is equal to or higher than themotion threshold THM, the flow proceeds to Step 1645; otherwise, theflow proceeds to Step 1640;

Step 1640: Does not generate the alarm signal; and

Step 1645: Generate the alarm signal.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. An image sensor, comprising: an event cameraincludes pixel units to generate pixel values in a high resolutionformat or a low resolution format; an image buffer, coupled to the eventcamera, for storing the pixel values; and a processing circuit, coupledto the even camera and the image buffer, for performing a motiondetection; wherein the event camera identifies an event according to achange of the pixel values in the low resolution format; and, after theevent is identified, the event camera stores the pixel values in thehigh resolution format into the image buffer and sends a trigger signalto wake up the processing circuit.
 2. The image sensor of claim 1,wherein the event camera is arranged for sensing at least one currentpixel value of the at least one pixel unit to detect whether the atleast one pixel value changes; when the at least one pixel valuechanges, the event camera triggers the processing circuit and transmitsinformation of the at least one pixel value to the processing circuit.3. The image sensor of claim 2, wherein when the at least one pixelvalue changes, the event camera further transmits a counter value to theprocessing circuit; the counter value corresponds to a time intervalbetween an event of the processing circuit entering the power savingmode and an event of the at least one pixel value changing; and, thecounter value is incremented by one and is not transmitted at a frametiming when the at least one pixel value does not change.
 4. The imagesensor of claim 2, wherein the information of the at least one pixelvalue and the counter value is stored into the image buffer before theprocessing circuit completely exits the power saving mode and enters anormal mode, to make the processing circuit after completely enteringthe normal mode perform the motion detection according to the countervalue and the information of the at least one pixel value which arestored in the image buffer.
 5. The image sensor of claim 2, wherein theevent camera is arranged for: determining that the at least one pixelvalue changes when at least one pixel difference between at least onereference pixel value of the at least one pixel unit and the at leastone current pixel value of the at least one pixel unit is higher than apixel threshold; generating the information of the at least one pixelvalue; outputting the counter value and the information of the at leastone pixel value to the processing circuit; updating the at least onereference pixel value as the at least one current pixel value; andresetting the counter value as zero.
 6. The image sensor of claim 2,wherein the event camera is arranged for: determining that the at leastone pixel value does not change when the at least one pixel differenceis lower than the pixel threshold; not outputting the counter value andthe information of the at least one pixel value to the processingcircuit; and accumulating the counter value by one.
 7. The image sensorof claim 1, wherein when the event camera determines that the at leastone pixel value changes, the event camera transmits a trigger signal towake up the processing circuit which is in the power saving mode.
 8. Theimage sensor of claim 1, wherein the information of the at least onepixel value is at least one actually captured value of the at least onepixel value.
 9. The image sensor of claim 1, wherein the information ofthe at least one pixel value is at least one difference value betweenthe at least one current pixel value and at least one previous pixelvalue of the at least one pixel unit.
 10. A method of an image sensor,comprising: providing an event camera including units to generate pixelvalues in a high resolution format or a low resolution format; providingan image buffer for storing the pixel values; providing a processingcircuit which is capable of performing a motion detection; using theevent camera to identify an event according to a change of the pixelvalues in the low resolution format; and after the event is identified,using the event camera to store the pixel values in the high resolutionformat into the image buffer and to send a trigger signal to wake up theprocessing circuit.
 11. The method of claim 10, further comprising:using the event camera to sense at least one current pixel value of theat least one pixel unit to detect whether the at least one pixel valuechanges; and when the at least one pixel value changes, using the eventcamera triggering the processing circuit and transmitting information ofthe at least one pixel value to the processing circuit.
 12. The methodof claim 11, further comprising: when the at least one pixel valuechanges, using the event camera further transmitting a counter value tothe processing circuit; wherein the counter value corresponds to a timeinterval between an event of the processing circuit entering the powersaving mode and an event of the at least one pixel value changing; and,the counter value is incremented by one and is not transmitted at aframe timing when the at least one pixel value does not change.
 13. Themethod of claim 11, wherein the information of the at least one pixelvalue and the counter value is stored into the image buffer before theprocessing circuit completely exits the power saving mode and enters anormal mode, to make the processing circuit after completely enteringthe normal mode perform the motion detection according to the countervalue and the information of the at least one pixel value which arestored in the image buffer.
 14. The method of claim 11, furthercomprising using the event camera: determining that the at least onepixel value changes when at least one pixel difference between at leastone reference pixel value of the at least one pixel unit and the atleast one current pixel value of the at least one pixel unit is higherthan a pixel threshold; generating the information of the at least onepixel value; outputting the counter value and the information of the atleast one pixel value to the processing circuit; updating the at leastone reference pixel value as the at least one current pixel value; andresetting the counter value as zero.
 15. The method of claim 11, furthercomprising using the event camera: determining that the at least onepixel value does not change when the at least one pixel difference islower than the pixel threshold; not outputting the counter value and theinformation of the at least one pixel value to the processing circuit;and accumulating the counter value by one.
 16. The method of claim 10,further comprising: when the event camera determines that the at leastone pixel value changes, using the event camera transmitting a triggersignal to wake up the processing circuit which is in the power savingmode.
 17. The method of claim 10, wherein the information of the atleast one pixel value is at least one actually captured value of the atleast one pixel value.
 18. The method of claim 10, wherein theinformation of the at least one pixel value is at least one differencevalue between the at least one current pixel value and at least oneprevious pixel value of the at least one pixel unit.
 19. An imagesensor, comprising: an event camera includes pixel units to generatepixel values in a high resolution format or a low resolution format; andan image buffer, coupled to the event camera, for storing the pixelvalues; wherein the event camera identifies an event according to achange of the pixel values in the low resolution format; and, after theevent is identified, the event camera stores the pixel values in thehigh resolution format into the image buffer and sends a trigger signalto wake up a processing circuit which is used to perform a motiondetection.
 20. The image sensor of claim 19, further comprising: theprocessing circuit, coupled to the even camera and the image buffer, forperforming the motion detection; wherein the event camera senses andoutputs at least one pixel value into the image buffer and determineswhether to generate and output the trigger signal; when the triggersignal is not outputted to the processing circuit, the sensed at leastone pixel value sent from the event camera is stored in the image bufferby using an image freeze operation; and, when the trigger signal isoutputted to the processing circuit, the sensed at least one pixel valuesent from the event camera is transmitted into the processing circuitand the image freeze operation is stopped.